The No.1 Website for Pro Audio
 All  This Thread  Reviews  Gear Database  Gear for sale     Latest  Trending
Loudspeakers and rooms - a scientific approach
Old 4 weeks ago
  #1
Gear Nut
 

Loudspeakers and rooms - a scientific approach

Hello all

What I'll present here is a short and simple abstract of the content of Floyd Toole’s book “Sound Reproduction”.

I feel far too few people are aware of the science behind loudspeakers and rooms and I will attempt here to guide those that feel an interest towards this subject. The ‘science’ started at the NRC in Canada and has evolved over many years to what we have today, which is excellent knowledge on the subject in no uncertain terms.
The results of this research are used by many brands the world over, some advertise it, others mention it in whitepapers, some simply use it without a word. The fact that many direct competitors make use of this research shows that the science works. Many end-users however are still in scientific dark-age. I hope to at least spark your interest with this post.

Frequently the topic on how to choose a monitor loudspeaker comes up. The answer is often that this is a personal choice, and depends on the room or even the genre of music you’re working on.

Although widely accepted, this information could not be more wrong. Although playback level, listening distance, and bass extension will play decisive role – the role of preference and even the room plays a smaller role than one might assume. Decades of scientific tests, correlating subjective measurements (blind listening tests) to technical measurements have concluded that independent of the room, listeners prefer loudspeakers that feature under anechoic conditions (!) a neutral (flat) direct sound, and smooth overall directivity. In practical terms if we have a series of loudspeakers that have been rated from good to bad in one room using blind testing, the overall score will differ from room to room, but they will not be rated differently. A good room can make a loudspeaker better, but it will not make a bad loudspeaker better than a good one.

The role of the monitor:

The role of the monitor is simply to provide us with an honest presentation of program material. To allow a monitor to function as intended it is necessary to know under what conditions this monitor was developed and what its intended use is. Many of what are referred to as ‘near-field’ monitors are still designed to function in a 4pi space. This means that they will function properly away from boundaries. Positioning them near boundaries (on consoles, desks, near screens, ..) will negatively affect their performance as these very early reflections will essentially become part of the direct sound – negating the (hopefully) neutral performance the manufacturer has worked hard to create.

Loudspeakers that are designed for 2pi (in-wall performance) subsequently will not perform well if used in free-space with regards to low frequency amplitude and diffraction effects.

Calibration and Translation:

Many systems are calibrated in-situ to a certain target curve. Some believe this to be as flat as possible, some believe in a custom (house) curve. To determine what is right, it is important to know how a loudspeaker behaves in a room. In practical terms, there is a part where the room dominates, and a part where the loudspeaker dominates. A good rule of thumb is to calculate the Schroeder frequency of your room, and up that one octave to find the so called ‘transition frequency’ of the room.

Below the transition frequency we can not separate the loudspeaker from the room, and the loudspeaker (or subwoofer) will behave as minimum-phase. This means we can use EQ to optimise the response at a certain position, make compromises and EQ over several positions – or use mode manipulation using several low frequency elements (subs) to minimize mean-spatial-variance over a larger space, which when combined with EQ will provide a good low frequency experience over a large part of the room.

Above the transition frequency, things get much trickier. Since our brain is now able to separate loudspeaker from the room (the direct from the reflected sounds). The truth is, since it has been established that loudspeakers that feature neutral performance under anechoic conditions are always preferred under blind listening conditions, that one should simply let them be. Even if the steady-state room curve is not flat, it is important to realize that the direct sound, responsible for our perception of timbre, is correct. The steady-state room curve will involve early and late reflections. With multi-way loudspeakers, depending on their orientation, there will always be a cancellation axis as one moves off-axis in the direction of the driver orientation. While a microphone is not able to discriminate between horizontal and vertical reflections, the latter being of much less importance to humans, since our ears are in the horizontal plane, these cancellations will show up in steady-state room measurements, almost always in the crossover region. Correcting these would change the direct sound (the first sound to arrive) and would make a good monitor worse.
If horizontal directivity is not optimal, this will also show in the steady-state room measurements. If the horizontal reflections are too dissimilar from the direct sound, this will be heard as coloration. Having neutral loudspeakers, both on- and off-axis will very much help in this regard.
Apart from these, there are other, often very local interference effects that could be ‘eq’ed out’ but would also alter the direct sound field, and again negatively affect timbre. On top of that, it would most certainly make the sound worse for any other listener in the room. It is also tempting to shelf up the treble range, however a slightly downward trend in steady-state is normal. The reflected high frequency sound are the first to be absorbed by air, any dampening in the room – and normal forward firing loudspeakers tend to spray more sound in the room as one drops in frequency (directivity index).

What does all of this mean in practical terms? It means that when following these guidelines, there is a very good chance that other people with good loudspeakers will hear your work as intended, meaning the content translates well. It is a tradition to ‘check’ mixes on lesser monitors such as Auratones, NS10s, .. simply put, this practice makes no sense. There are an infinite number of ways a loudspeaker can have faults, but neutral is universal. Making a mix sound decent on a bad speaker will more often than not create an inverse of that particular loudspeaker’s faults, making the mix sound worse on a capable system.

Time domain performance

“We do not hear waveforms, whether they are impulses, steps, square waves or any voice or instrument of music” – F.E. Toole.

As it turns out, humans are essentially phase-deaf in absolute terms. We can very much measure things we simply cannot hear. We respond very well to changes in amplitude response, but are generally insensitive to phase shifts. Phase matters in loudspeakers in multi-way systems where you would expect it to. In crossovers where phase inbetween drivers can interfere, and the reason that we are sensitive to this is, you’ve guessed it, because it will affect the amplitude (frequency response). In this regard we can assume phase also matters between loudspeakers as to create phantom images from mono signals.

F.E. Toole on low frequency ringing: “Room resonances at low frequencies behave as “minimum phase” phenomena, and so, if the amplitude vs. frequency characteristic is corrected, so also will the phase vs. frequency characteristic. If both amplitude and phase responses are fixed, then it must be true that the transient response must be fixed – i.e. the ringing, or overhang, must be eliminated”


Conclusion:

Loudspeakers with a neutral (flat, free of resonances) direct sound field and well behaved directivity characteristics, positioned correctly in a good acoustical environment, and calibrated below the transition frequency, should provide an excellent mixing environment, ensuring translation and listening pleasure. It is a fact that loudspeakers no longer have to be the limiting factor in performance. In many cases, it has now become the program material.

It is time to step away from the circle of confusion



And into the orbit of order



I hope my post will spark some interest, introduce some polite discussion - and hopefully be of help for those of you confused and struggling - for those of you trapped in that circle of confusion.

Last edited by Fhorn88; 4 weeks ago at 06:31 PM.. Reason: typo
Old 4 weeks ago
  #2
Lives for gear
Hello,

Floyd Toole is well known in the acoustic forum and a great reference in acoustic and speaker design.
Old 4 weeks ago
  #3
Gear Nut
 

Comparing and selecting monitors

Comparing loudspeakers in a room requires forethought and considerations. Placing pairs of loudspeakers in a room in different physical positions, adding to that knowing what is playing, completely invalidates the test from an objective point of view. First of all bass performance of a loudspeaker as we have determined is dominated by room effects. Listening to loudspeakers in different physical positions will alter the frequency response at any given position. Since bass performance accounts for around 30% of preference ratings, this just may tip the scales when comparing two similarly well performing models (from an anechoic point of view).

Sighted bias is strong and many tests with enthousiasts and professionals alike have resulted in the same outcome, namely that it (bias) cannot be avoided. Therefore the only reasonable action is to perform the test blind. Level matching is a good idea, although since no two loudspeakers will exhibit the exactly the same frequency response or directivity pattern, exact matching may not be possible. Luckily this does not seem to matter as loudspeakers with the fewest amount problems in terms of resonances, directivity and overall frequency response, are still recognizable.

Research has also shown that the more sources and reflections are added, the less sensitive we become to certain issues. Therefore loudspeaker testing should be performed in mono, using one loudspeaker. Concerns may arise about not being able to compare subjective matters, such as “imaging” – although research again shows that preference ratings between loudspeaker do not vary from mono to stereo, although it takes listeners longer to reach the same conclusion.

Pre-selecting monitors should be done using comprehensive, high-resolution anechoic measurements. More and more manufacturers are making these available, independent tests are also valuable sources (soundandrecording springs to mind). Keep in mind your listening distance, low frequency extension, overall spl capabilities, and how you plan on placing them in the room. As mentioned before, loudspeakers, unless specifically developed for usage under those circumstances, should be placed relatively free from boundaries and other adjacent surfaces (such as consoles, desks, screens, ..).

For the actual comparison, which needs to be performed blind as we’ve determined, a switch box and an assistant will be necessary. Ideally you will have access to some sort of rotating platform so that the assistant can easily switch between 3 to 4 loudspeakers, while keeping the physical position identical. Switches need to be as quick as possible since auditory memory is not great. If such a platform is not available, the loudspeakers may be positioned next to eachother, but will have to be switched around over several rounds so that each loudspeaker will have played once in each position, so that an average score can be achieved. Adding one technically faulted loudspeaker that does not have a neutral on and/or off-axis response can help put certain matters into perspective. The loudspeakers should be placed with their respective acoustical axis at ear level and on-axis.

Since program material may have imprinted the inverse of whatever the amplitude response was of the loudspeakers that were part in the process of making it, it is important to use a variety of recordings as to exclude any bias or advantage in this department.

This may seem like a daunting undertaking, but when you are spending (potentially) a lot of money, a day of work is nothing in compared to the results.
Old 4 weeks ago
  #4
Lives for gear
 
Brian M. Boykin's Avatar
I’ve been making my way through Floyd Toole’s book and this is very helpful. You’ve connected a lot of dots. I’m in the process of treating and measuring my room and this is timely. Thank you.
Old 4 weeks ago
  #5
Lives for snowflakes
 
12ax7's Avatar
 

Quote:
Originally Posted by Fhorn88 View Post
"The role of the monitor is simply to provide us with an honest presentation of program material."
That sounds pretty simple, eh?
(Funny how these things work out, ain't it?)
.
Old 4 weeks ago
  #6
Gear Nut
 

Quote:
Originally Posted by 12ax7 View Post
That sounds pretty simple, eh?
(Funny how these things work out, ain't it?)
.


I guess it frustrates me that for many people monitoring seems to be hit or miss. I've read pages with subjective opinions on this forum, more often than not inaccuracies. Read about many sighted monitoring tests, which basically holds little value from an objective point of view (sorry!).

Most people seem to be open-minded and at least ponder about this different approach. The problem is more often than not the veterans, who have been in the business for many years, who have firm beliefs and a definite way of doing things - even if it is objectively wrong.

For many people when it comes to monitoring it's usually a blaming game with the subject being why the material is not translating well/why the monitors sound tiring/why the monitors sound foggy. Hence, I will try my best to outline certain matters according to what objective research tells us, and hope that it will be of help for some of the people here.
Old 4 weeks ago
  #7
Gear Nut
 

Early reflections

In a basic sense, the early reflections consist of the 6 first reflection points - the two sidewalls, the front and back wall, and the floor and ceiling. Since our ears are in the horizontal plane to the side of our head, the sidewall reflections are in general of more importance to us. The human hearing system is complex, and not everything that an omnidirectional microphone can capture is of equal importance to us.

Room acoustics are a different topic than loudspeakers, yet they must coexist. Rooms, believe it or not, are good for sound reproduction. Two ears and a brain have the ability, above the transition frequency to 'listen through rooms'. We can subconsciously tell apart what the speaker is doing, and what the room is adding. This is why in double-blind tests, relative rating inbetween loudspeakers manages to stay constant. This is very good news for reproduction at home, as this means that in broad lines, people will be able to enjoy similar sound quality at home, as the one you have while creating the content - if you've followed the guidelines that is.

There are however some differences between studio monitoring and leisured playback. Studios are often heavily treated, unlike living rooms. Many people working on recording want to eliminate room influences as to be able to pick up on small details otherwise masked. Before moving forward let us take a short look back at how this came to be.

In older days, technology regarding sound reproduction was limited, and the relation between loudspeakers and rooms was less understood. Many of the old standards (Altec 604, UREI, ..) did not heave good on-axis performance, and overall terrible off-axis performance - The only way to make a bad situation better was to absorb these reflected sounds as much as possible. The birth of the dead-end control room. In the end engineers started placing smaller loudspeakers on their consoles to get even more direct sound (which unkowingly brought about other issues of course).

Both knowledge of loudspeakers and acoustics have much improved since the old days.
If you know what to look for, it is possible to find loudspeakers that feature both neutral on- and off-axis performance - meaning that reflections are not necesserily perceived as colouration of the direct sound field. So what to do?

We have three options to consider. Diffuse - Absorb - Reflect

Whichever one you choose, make sure to do it for as much of the bandwith as possible. Down to the transition frequency at least. Why? Otherwise the reflection is not being scattered, or absorbed, but merely altered. In case of a loudspeaker with a neutral off-axis behaviour, you have potentially made the reflected sound worse than it was to begin with.
Since diffusion down to the transition frequency is very difficult, this leaves us, in practical terms, with absorption or reflection. Whichever you choose, is up to you (and may be influenced by the off-axis behaviour of your loudspeaker), but do it right.

Should you absorb to play it safe? Difficult to say. Neutral early reflected sound has been shown to improve crosstalk effects from stereo loudspeaker systems, enhance ASW - and in many cases will be more similar to playback at home, potentially improving 'translation'.
The choice is up to you.
Old 4 weeks ago
  #8
Gear Nut
 

Comprehensive loudspeaker measurements

As we've determined in-room, in-situ, full range loudspeakers measurements are not very useful for determining loudspeaker performance. Comprehensive anechoic, high-resolution measurements are needed to make an informed decision.

If manufacturers decide to share frequency response it is usually a single on-axis measurement, often smoothed to some degree. This, along with a generous verrtical scale can produce a fairly flat visual line, without telling you much about this loudspeaker. It doesn't even tell you a lot about the on-axis measurement itself. Look for high-resolution (1/20 octave smoothing or better) data, normalised to a 45 to 105dB vertical scale in 5dB increments (standard). . A standard measurement is performed at 2m with a 2.83v input signal, the measurement is later normalised for sound pressure level at 1m. 2m is standard because in multi-way loudspeakers (especially 3 or more way models) sufficient distance is required for individual drivers to blend.

The on-axis response curve, as the name states, is one measurement taken directly on the acoustical axis of a loudspeaker. It is the most frequently used curve, but in itself not very valuable. To put this on-axis response into perspective, more information is needed.

A single point measurement has the added disadvantage that it can introduce certain, otherwise harmless, artifacts. A more modern method is use an average of measurements that more accurately represents the direct sound field. The ANSI 2034 standard uses a +/-30° horizontal and +/-10° vertical as the 'listening window' If you can find this information, or something close to it, it is valuable since the direct sound is critical and should be neutral. It should be close to the on-axis sound, save some minor artifacts. If the listening window average, and on-axis sound, are quite apart, it means the loudspeaker will be very directional and even a slight positional change will alter the sound. Never a good thing.

This brings us to the indirect sound. The first of indirect sound to arrive at our ears, are the early reflections. As stated the above, they consist of lateral reflections, front and rear wall reflections, and floor and ceiling reflections. Due to the orientation and physical location of our ears, the lateral reflections are of special importance to us. Luckily, when manufacturers specify off-axis data, it is usually this particular data. Since the early lateral reflections tend to occur far off-axis the 50° to 80° information is particularly useful.

Unless you opt to eliminate them (which the previous post explains), it is crucial that these reflect the listening window curve closely with either constant or gradually changing directivity, depending on the design of your monitor. If there are directivity issues, it would be better to eliminate these reflections for critical monitoring purposes.

The ANSI 2034 standard features a weighted average of all the early reflected sounds in a single curve. Since these also encompass vertical reflections, small, harmless irregularities can come forward that are otherwise harmless and inaudible. To elaborate: In any multi-way loudspeaker system, for a given driver orientation, cancellation occurs as one moves in the direction of the orientation, and the drivers become out of phase with one another. Since this does not appear in the direct sound field, and our hearing system is not well optimised for vertical listening, these effects are harmful and inaudible. If you believe otherwise, do a blind test as described in the earlier post, and be your own judge.

The final metric is total sound power, a weighted average of the sound leaving in all directions. Sound power is useful for confirming resonances. A true resonance will exist in all the curves. It is also useful for calculating the directivity index of your loudspeaker. The sound power DI is the difference between the sound power curve, and the listening window (or on-axis curve in some cases) in dB. The DI should be smooth and gradually changing, or of constant directivity depending on your type of monitor. In the ANSI 2034 standard the early reflections average curve is also used to calculate the early reflection directivity index, the difference between it and the listening window curve in dB.

More information on the ANSI 2034 standard: https://www.sausalitoaudio.com/wp-co...ama-Charts.pdf

If you've read this post carefully: congratulations! I hope it will be of help in your quest to finding a better monitor, although I understand many manufacturers do not share this data. Ask yourself why this is though. If it does not exist, something is wrong. If they won't share it, it may not be worth sharing - or another division (marketing) is keeping engineering from showing it. When spending money, sometimes a whole lot of it, this data needs to be made available to make a well thought out choice. Don't take anyone's word for it. Know what you are possibly purchasing.
Old 4 weeks ago
  #9
Lives for gear
 
Brian M. Boykin's Avatar
This is making complete sense. As someone who’s invested in a measurement mic and is currently using REW to take measurements, how would I go about (or is it even possible) to measure off axis reproduction of my monitors?

One thing that pops into my head to measure is the SPL at the listening position as well as at the absorption face of the side wall first reflections. Shortening the direct sound distance and lengthening the distance to the side wall first reflections will help, however, you have to have the direct sound distance in the sweet spot for the particular monitor to be sure the drivers are blending properly.

Am I interpreting this info correctly?

Also, I’m going with a Davis and Davis model of absorption in the first half of the room. I also have back wall absorption in the first reflections.

I’m going to recalculate the transition frequency for my room to see how close I am to covering frequencies above it with absorption.

Thank you again for posting this. I’m gleaming from it.
Old 4 weeks ago
  #10
Gear Nut
 

Quote:
Originally Posted by Brian M. Boykin View Post
This is making complete sense. As someone who’s invested in a measurement mic and is currently using REW to take measurements, how would I go about (or is it even possible) to measure off axis reproduction of my monitors?

One thing that pops into my head to measure is the SPL at the listening position as well as at the absorption face of the side wall first reflections. Shortening the direct sound distance and lengthening the distance to the side wall first reflections will help, however, you have to have the direct sound distance in the sweet spot for the particular monitor to be sure the drivers are blending properly.

Am I interpreting this info correctly?

Also, I’m going with a Davis and Davis model of absorption in the first half of the room. I also have back wall absorption in the first reflections.

I’m going to recalculate the transition frequency for my room to see how close I am to covering frequencies above it with absorption.

Thank you again for posting this. I’m gleaming from it.
Hi Brian

Glad to see someone finds the information useful. I'll try to answer your questions.

-It is certainly possible, although not always practical depending on how low you need accurate information. Can you share your some information of your monitor setup? Using a combination of nearfield and/or gated measurements it should be possible to achieve decent resolution down to below 1kHz - since most directivity issues stem from non-matched drivers, and most crossovers (save large 2-ways involving horns) are above this point, useful information can be retrieved this way. In fact if you should perform these measurements, it's useful to produce the on-axis and listening windows curves as well - you never know they may be of use.


-It would be possible that way. For mid/high measurements on the acoustical axis (usually between mid and tweeter - sometimes tweeter.. consult your manual) often 30cm is enough to get some valid information. Again since most of the directivity issues will happen above that 1kHz point, it's a useful technique.
Edit: even if only measuring one certain angle - make several measurements spaced a little bit apart to average potential interference effects.


And good luck! If you can 'borrow' a loudspeaker with known specs (a Neumann KH80 is a good candidate) you can practice your measurement techniques.

Last edited by Fhorn88; 4 weeks ago at 07:38 PM.. Reason: added info
Old 4 weeks ago
  #11
Lives for gear
 
Brian M. Boykin's Avatar
Main monitors are Event 20/20 bas v1’s. They’re a two way design featuring a 1” HF driver with an 8” LF driver. Acoustical crossover at 2.6kHz. I have been unable to find any data as to their axis and off axis specs. They are considered a direct field monitor per the manual.

The manual does not give a minimum distance required for the drivers to blend properly. It does state an equilateral triangle is preferred and placed “slightly behind and to either side of a small console.” This leads me to believe a 3ft to 6ft spread depending on what “small console” means to you in your world.

As for my goals? The flattest response I can get (or house curve) the room will allow. Meaning, I’m just gonna keep going till I max it out. I’ve calculated room volume at 1550 cubic feet so the low end will never be perfect. But as you say, there should be a reasonable expectation for how low I can achieve. Room dimensions at 120”H x 147”W x 167”L. The ceiling is vaulted on three of the sides. The rear wall extends straight to the ceiling with no vault. One of my struggles is a cavity in the front wall that’s approximately 7ft wide, by 8ft high, by 16.6” deep. Plan is to flush mount the monitors into this cavity with a soft front wall doubling as a bass trap. Picture provided below.

I also have a set of Yamaha NS500m’s I also plan to flush mount above the monitors and computer monitor in the pic. These are more for checking the low end and to feel the music rather than serious monitoring for tracking and mixing. They will take up considerable area above the main monitors.
Attached Thumbnails
Loudspeakers and rooms - a scientific approach-fac10d1e-4ee7-47fa-9749-25c5670a988d.jpg  
Old 4 weeks ago
  #12
Gear Nut
 

My first advice would be to put them in the correct orientation - vertical. It may be necessary to flip them (putting the tweeter at the bottom) or aim them down so that the acoustical axis aims towards ear height. What will happen in the current orientation is that there will be phase issues inbetween drivers as you move off-axis. If you absorb the lateral reflections, this is not a problem for the reflected sounds, BUT, your listening window will be a lot narrower than if you were to use them as intended, which will be rewarded with a wider sweet spot.

Second, since we know the steady-state measurements (usually made at the listening position) don't give us much useful information above the transition frequency, make those nearfield measurements of the on-axis and listening window I mentioned in my previous post. If performed correctly, those would form a good base for EQ. If you can get the listening window flat, that's all you need to worry about with that loudspeaker really. We cannot change directivity. EQ at the listening position should be reserved for below the transition frequency only. Good luck!

Last edited by Fhorn88; 4 weeks ago at 05:39 PM.. Reason: typo
Old 4 weeks ago
  #13
Lives for gear
 

Quote:
Originally Posted by Fhorn88 View Post
(...) EQ at the listening position should be reserved for below the transition frequency only (...)
could you pls expand a little bit on that (in non-technical terms)?
Old 4 weeks ago
  #14
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by Fhorn88 View Post
My first advice would be to put them in the correct orientation - vertical. It may be necessary to flip them (putting the tweeter at the bottom) or aim them down so that the acoustical axis aims towards ear height. What will happen in the current orientation is that there will be phase issues inbetween drivers as you move off-axis. If you absorb the lateral reflections, this is not a problem for the reflected sounds, BUT, your listening window will be a lot narrower than if you were to use them as intended, which will be rewarded with a wider sweet spot.

Second, since we know the steady-state measurements (usually made at the listening position) don't give us much useful information above the transition frequency, make those nearfield measurements of the on-axis and listening window I mentioned in my previous post. If performed correctly, those would form a good base for EQ. If you can get the listening window flat, that's all you need to worry about with that loudspeaker really. We cannot change directivity. EQ at the listening position should be reserved for below the transition frequency only. Good luck!
I’ll try them set vertically. The manufacturers own literature states they can be placed vertically or horizontally with no effect of the listening window, however, testing will give the definitive answer. Those stands in the picture are custom built and filled with cinder blocks. Each one weighs in at approximately 200lbs. I’d have to cut them down. Nothing I couldn’t do in a couple hours, but I’d really like to avoid it.

I’ve been reading a lot on this subject since your first post. You’ve opened my eyes to another aspect of acoustics I hadn’t thought of. I’m considering a complete monitor upgrade now that I understand the importance of the drivers on and off axis characteristics. I’m gonna play with measuring in REW and see if I can get any useful data.
Old 4 weeks ago
  #15
Gear Nut
 

Quote:
Originally Posted by Brian M. Boykin View Post
I’ll try them set vertically. The manufacturers own literature states they can be placed vertically or horizontally with no effect of the listening window, however, testing will give the definitive answer. Those stands in the picture are custom built and filled with cinder blocks. Each one weighs in at approximately 200lbs. I’d have to cut them down. Nothing I couldn’t do in a couple hours, but I’d really like to avoid it.

I’ve been reading a lot on this subject since your first post. You’ve opened my eyes to another aspect of acoustics I hadn’t thought of. I’m considering a complete monitor upgrade now that I understand the importance of the drivers on and off axis characteristics. I’m gonna play with measuring in REW and see if I can get any useful data.
A simple tilt-down would be sufficient, no need to cut into anything Just make sure the acoustical axis 'points' towards your ear height. That's it.
Vertical vs horizontal: It's physics really. In a vertically oriented driver configuration, moving along that axis will put the drivers out of phase more and more as one moves away from the acoustical axis point. At certain points you even reach a complete cancellation. Here's a little sketch for a LR4 filtered two-way

Old 4 weeks ago
  #16
Gear Nut
 

Quote:
Originally Posted by deedeeyeah View Post
could you pls expand a little bit on that (in non-technical terms)?
In my first post there is a paragraph 'calibration and translation'. I hope it's not too technical, otherwise - ask away if I need to clarify anything.
Old 4 weeks ago
  #17
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by Fhorn88 View Post
A simple tilt-down would be sufficient, no need to cut into anything Just make sure the acoustical axis 'points' towards your ear height. That's it.
Vertical vs horizontal: It's physics really. In a vertically oriented driver configuration, moving along that axis will put the drivers out of phase more and more as one moves away from the acoustical axis point. At certain points you even reach a complete cancellation. Here's a little sketch for a LR4 filtered two-way

Can’t I use pink noise and my measurement mic and put REW in spectrum analyzer and move the mic horizontally through the Acoustical window to see how it’s affected? I could also get an idea of how wide the window is, where it starts and where it ends, correct?
Old 4 weeks ago
  #18
Lives for gear
 

Quote:
Originally Posted by Fhorn88 View Post
In my first post there is a paragraph 'calibration and translation'. I hope it's not too technical, otherwise - ask away if I need to clarify anything.
it's not that i wouldn't get it (but i assume some less experienced folks could struggle a bit) or that i'd use inferior gear or have suboptimal room treatment (5 studios, professionally designed), it's that i've been measuring/analyzing/correcting/aligning dozens of monitoring systems of studios and permanent installs (and thousands of pa systems) for 35 years by using external speaker processors (for ca 20 years now) and i'd like to hear further arguments why not to correct fr all the way up...

btw: not interested in expanding to pa's: conditions/goals are mostly vastly different from studio environments (although things get interesting when setting up temporary monitoring systems in relatively large but acoustically subpar rooms for location recording...)!
Old 4 weeks ago
  #19
Gear Nut
 

Quote:
Originally Posted by Brian M. Boykin View Post
Can’t I use pink noise and my measurement mic and put REW in spectrum analyzer and move the mic horizontally through the Acoustical window to see how it’s affected? I could also get an idea of how wide the window is, where it starts and where it ends, correct?
You could. Individual sweeps with 1/24 octave smoothing would provide you with some more detailed graphs. Be sure to do this in the nearfield as you don't want any reflections in your measurements for this purpose.
Old 4 weeks ago
  #20
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by Fhorn88 View Post
You could. Individual sweeps with 1/24 octave smoothing would provide you with some more detailed graphs. Be sure to do this in the nearfield as you don't want any reflections in your measurements for this purpose.
Got it. The mic should be pointed on axis rather than at the ceiling like when testing the room, correct? And one speaker at a time, correct?
Old 4 weeks ago
  #21
Gear Nut
 

Quote:
Originally Posted by deedeeyeah View Post
it's not that i wouldn't get it (but i assume some less experienced folks don't) or that i'd use inferior gear or have suboptimal room treatment (5 studios, professionally designed), it's that i've been measuring/analyzing/correcting/aligning dozens of monitoring systems of studios and permanent installs o (and thousands of pa systems) for 35 years now by using external speaker processors (for ca 20 years now) and i'd like to hear further arguments why not to correct fr all the way up...
As explained, because our hearing system seperates direct from reflected sounds in a room above the transition frequency. Corrections based on the measured sum is correcting based on the wrong information. One could have a neutral direct sound field, yet not see that in a simple measurement. By 'correcting' that measurement, you alter the direct sound, potentially making the situation worse.

The only certainty is in using loudspeakers that measure well from an anechoic point of view, and leaving them be above the transition frequency. It's impossible to reverse engineer what a loudspeaker is doing using in-situ full range measurements.
Old 4 weeks ago
  #22
Lives for gear
 

Quote:
Originally Posted by Fhorn88 View Post
(...) potentially making the situation worse (...)
it's this i cannot relate to as you're making an assumption which is not necessarily true:

what would you tell all the happy trinnov users (or my clients, using different processors) who - subjectively - experience an inprovement in the overall behaviour of their monitoring system although most got tweaked (to various degrees, some of them quite heavily) and many of them using a target curve which includes filters affecting a very wide frequency range (and especially the hf)?

Last edited by deedeeyeah; 4 weeks ago at 07:34 PM.. Reason: typo
Old 4 weeks ago
  #23
Lives for gear
 
Brian M. Boykin's Avatar
What is the variable that drives the translation frequency lower? 250hz seems to be a good rule of thumb when reading up on it. I looked at some REW FR graphs for my room when I was experimenting and some have it at 80hz and others at 104hz which is probably evidence that my tests are flawed.

What you say?
Old 4 weeks ago
  #24
Gear Nut
 

Quote:
Originally Posted by deedeeyeah View Post
it's this i cannot relate to as you're making an assumption which is not necessarily true:

what would you tell all the happy trinnov users (or my clients) which (sujectively) experience an inprovement in the overall behaviour of their monitoring system although most got tweaked (to various degrees, some of them quite heavily) and many of them using a target curve which includes filters affecting a very wide frequency range (and especially the hf)?
1) Since those corrections also involve the low range, and around 30% of our subjective preference rating comes down to low frequency performance (smoothness, exention), and since equalization below the transition frequency is benficial, I would say that this alone could improve upon the original situation

2) Since not all loudspeakers (even some very expensive ones) are made equal, it is possible that you have improved upon the original situation, if the loudspeaker was not anechoically neutral to begin with.

3) Question: Is your target curve the same for every room?

4) I would tell them, and anyone, that it can be done differently, with better results -as I'm advocating for in this thread.
Old 4 weeks ago
  #25
Gear Nut
 

Quote:
Originally Posted by Brian M. Boykin View Post
What is the variable that drives the translation frequency lower?

Room size. The larger, the lower.

http://www.acoustic.ua/forms/room-modes-eng.html
Old 4 weeks ago
  #26
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by Fhorn88 View Post
Room size. The larger, the lower.

http://www.acoustic.ua/forms/room-modes-eng.html
Been on that page before. It has it at 203hz, however, my room has vaulted ceilings. I would assume that will affect the calculations and would drive it a little higher because of the loss of volume. Am I correct in thinking so?
Old 4 weeks ago
  #27
Gear Nut
 

Quote:
Originally Posted by Brian M. Boykin View Post
Been on that page before. It has it at 203hz, however, my room has vaulted ceilings. I would assume that will affect the calculations and would drive it a little higher because of the loss of volume. Am I correct in thinking so?
That would be correct. A good rule of thumb were to correct up to between 400 and 500Hz
Old 4 weeks ago
  #28
Gear Nut
 

Quote:
Originally Posted by Fhorn88 View Post
That would be correct. A good rule of thumb were to correct up to between 400 and 500Hz*
*Based on measurements from the listening position
Old 4 weeks ago
  #29
Lives for gear
 
Brian M. Boykin's Avatar
Quote:
Originally Posted by Fhorn88 View Post
*Based on measurements from the listening position
Got it. I have 4 boxes of Corning 703 in the garage. Room is on hold while I sort this all out. Great information. I spent roughly 4 to 5 months reading up on room acoustics prior to moving into my new room. The info you’ve provided has cleared up some fog. Your giving the “reason”’for a lot of advise I’ve read on the Acoustical forum. A lot of times the advise comes in the way of “do this” with a short version of the reason why. This is taking it to the monitors themselves and how they are designed. ??
Old 4 weeks ago
  #30
Gear Nut
 

Quote:
Originally Posted by Brian M. Boykin View Post
This is taking it to the monitors themselves and how they are designed. ??
Absolutely - at the very least the direct sound field needs to be neutral. The problem is the lack of credible information provided by manufacturers. As Toole points out "There is more objective information on a $100 tyre than on you tend to get with $10000 speakers". It's true, and it is absurd.

In the absence of this, we're left with making our own measurements, trying to replicate anechoic data, as well as we possibly can.

Full range equalization is a guessing game at best. It's impossible to reverse-engineer what the loudspeaker is doing, and what the room is doing, from the listening-position, with accuracy (which is needed). A good room curve doesn't necessarily make a good loudspeaker, but a good loudspeaker will produce a good looking room curve if set-up properly.

Here's an active loudspeaker I designed myself. Black = on axis / Green = Listening window / Red = early reflections according to the ANSI 2034 standard. These are the 'anechoic measurements' above 800Hz

The picture below it, is the response at the listening position, with no EQ above 300Hz

Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump